Atrial fibrillation is a condition in which upper chambers of the heart beat rapidly and irregularly. One known manner of treating atrial fibrillation is to administer drugs in order to maintain normal sinus rhythm and/or to decrease ventricular rhythm. Known drug treatments, however, may not be sufficiently effective, and additional measures such as cardiac tissue ablation must often be taken to control the arrhythmia.
Known ablation procedures for treating atrial fibrillation include performing transmural ablation of the heart wall or adjacent tissue walls using radio frequency (RF) energy. One known ablation procedure involves burning or ablating cardiac tissue and forming lesions to break up circuits believed to drive atrial fibrillation.
The use of RF energy for ablation may, however, lead to untoward healing responses such as collagen build up at the area of interest after treatment. RF ablation within an atrium may also decrease atrial output. Thus, while RF transmural ablation has been used effectively in the past, cryogenic ablation has received increased attention for treatment of atrial fibrillation in view of the effectiveness of cryo-ablation procedures with fewer side effects.
One known endocardial cryo-ablation procedure involves inserting a catheter into the heart, e.g., through the leg of a patient. Once properly positioned, a portion of the catheter, typically the tip of the catheter, is cooled to a sufficiently low temperature by use of a liquid coolant or refrigerant such as nitrous oxide, e.g., to sub-zero temperatures of about −75° C., in order to freeze tissue believed to conduct signals that cause atrial fibrillation. The frozen tissue eventually dies so that the ablated tissue no longer conducts electrical impulses that are believed to cause or conduct atrial fibrillation signals.
Certain known endocardial cryo-ablation devices include expandable balloons, which are inflated with the liquid coolant or refrigerant. After the ablation is performed and before the device is withdrawn from the patient, the balloon is deflated and retracted into a guide sheath.
However, after expanding the balloon, performing the ablation procedure, and deflating the balloon, a user may encounter difficulties in retracting the deflated balloon into the guide sheath due to the balloon having a profile that is too large to re-enter the sheath. In particular, prior to inflation, the balloon profile is at its smallest, but after inflation has occurred, the balloon material is free to expand and may bunch up at the tip of the sheath during retraction of the balloon into the sheath. Thus, increased force is required to retract the deflated balloon, thereby potentially damaging the balloon during the balloon retraction procedure.